1. Field of the Invention
This invention relates to a device for transporting and distributing a liquid, and more particularly to an ionic activity measuring device which comprises the liquid transporting and distributing device and which is useful for potentiometric measurement of the concentration or ionic activity of an ion contained in liquid samples, such as water, body fluids (for example, whole blood, blood plasma, blood serum, urine and the like), and aqueous solutions (for example, wine, beer and the like).
2. Description of the Prior Art
Generally, from the clinical or industrial point of view, it is important to selectively measure the concentration or ionic activity of an inorganic ion, for example K.sup..sym., Na.sup..sym., Ca.sup.2.sym., Cl.sup..crclbar., or HCO.sub.3.sup..crclbar., contained in body fluids or aqueous solutions. For this purpose, it has been proposed to use dry type, ion-selective electrodes, which are easy to store and operate, for measurement. As an example of the dry type, ion-selective electrode (half cell or single electrode), it has been proposed in Japanese Unexamined Patent Publication No. 52(1977)-142584 (corresponding to U.S. Pat. Nos. 4,053,381 and 4,214,968) to coat or laminate four functional layers on a substrate and form a film-like, dry type, solid ion selective electrode. (Hereinafter sometimes referred to as the solid electrode). To conduct measurement with the film-like, solid electrode of this type, a very small amount (e.g. between 5 .mu.l and 50 .mu.l) of a liquid sample is applied to a predetermined position on the solid electrode.
FIG. 1 is a schematic perspective view showing a conventional film-like, solid, ion-selective electrode comprising four coated or laminated functional layers. In FIG. 1, a solid electrode 10 comprises a metal layer 11, a water-insoluble metal salt layer 12, a reference electrolyte layer 13 and an ion-selective layer 14 sequentially coated or laminated as the functional layers on a substrate 19. For example, the metal layer 11 is formed of silver, the water-insoluble metal salt layer 12 is formed of silver chloride, the reference electrolyte layer 13 is made by dispersing potassium chloride in a hydrophilic organic polymer binder, and the ion-selective layer 14 is an organic ion selective layer containing an organic compound capable of selectively responding to a predetermined ion, a carrier solvent and an organic polymer binder.
It has also been proposed in Japanese Unexamined Patent Publication No. 57(1982)-17851 to use a solid electrode comprisng three coated or laminated functional layers, in which the reference electrolyte layer 13 shown in FIG. 1 is omitted, and the ion-selective layer 14 consisting of organic materials is directly positioned on the water-insoluble metal salt layer 12. Further, Japanese Unexamined Patent Publication No. 48(1973)-82897 (U.S. Pat. No. 4,115,209) discloses a dry type, solid electrode comprising two coated or laminated functional layers, in which the water-insoluble metal salt layer 12 and the reference electrolyte layer 13 shown in FIG. 1 are omitted, and an ion-selective layer 14 containing an ion exchange material is positioned directly on the metal layer 11.
The ion-selective layer 14 is essential if the ion to be measured is K.sup..sym., Na.sup..sym., Ca.sup.2.sym. or HCO.sub.3.sup..crclbar.. If the ion to be measured is Cl.sup..crclbar. and the electrode comprises a metal layer 11 made of silver and an insoluble metal salt layer 12 made of silver chloride, it is possible to replace the ion-selective layer 14 with a protective layer made of, for example, cellulose acetate, polymethacrylic acid, polyacrylic acid, or poly(2-hydroxyethyl acrylate) employed in a halogen ion-permeable protective layer as disclosed in Japanese Unexamined Patent Publication No. 55(1980)-89741 (corresponding to U.S. Pat. Nos. 4,199,411 and 4,199,412).
When the ionic activity is determined by use of two solid electrodes described above, they are connected with each other by a bridge described later, and a potentiometer is connected therebetween. Then, a sample and a standard solution respectively are spotted onto the solid electrodes, and the difference in potential between the electrodes which is indicated on potentiometer is read to determine the activity of an ion contained in the sample solution. In this case, these solid electrodes must be electrically isolated from each other.
FIG. 2 is a schematic perspective view showing a conventional ionic activity measuring device comprising two film-like, solid electrodes of the type described above, as disclosed in FIGS. 4-5 of Japanese Unexamined Patent Publication No. 52(1977)-142584 (FIGS. 8-10 of U.S. Pat. No. 4,053,381). In this conventional device, in order to electrically isolate two solid electrodes 10 from each other, they are put in spaced relation to each other in a frame 30 made of a non-conductive material such as a plastic, and a bridge 201 defined by a groove coated with a surface active agent and having an open top side which extends between the electrodes 10. In FIG. 2, the bridge 201 defined by a groove is positioned between holes 28 and 29 at the respective solid electrodes 10.
FIG. 3 is a schematic perspective view showing another conventional ionic activity measuring device, as disclosed in Japanese Unexamined Patent Publication No. 55(1980)-20499 (U.S. Pat. No. 4,184,936). In FIG. 3, a hole 233 is formed in the upper surface of a flat member 31, and a bridge 20 provided with holes 28 and 29 are positioned in the hole 323, so that an ion can be transported between electrodes 10. The bridge 20 is of the type generally called the capillary bridge, which is used to promote ion transport between the electrodes 10.
FIG. 4 is a sectional view taken along the line S--S in FIG. 3. The capillary bridge 20 is formed of a three-layer laminate of various configurations. As shown in FIG. 4, the bridge 20 is constituted by three flat strips through which the holes 28 and 29 are perforated. Droplets of solutions 41 and 42 are applied to the holes 28 and 29, respectively. The capillary bridge 20 comprises a non-porous bottom substrate 22 existing nearest to the solid electrode, an intermediate porous layer 21, and a top non-porous hydrophobic layer 24 existing farthest from the solid electrode.
To prevent the functional layers of the electrodes 10 from being short-circuited at their edges due to the sample or the standard solution bleeding out of the bridge 20, the bridge 20 is sealed from the electrodes 10 at least at the circumferences of the holes 28 and 29.
The intermediate porous layer 21 is made, for example, of porous paper, a membrane filter, threads, a fabric or the like. The layer 21 absorbs the liquid droplets 41 and 42 and causes them to contact each other, resulting in ion transport. When liquid droplets are applied to the holes 28 and 29, the droplets fill up the holes, form a large "lid" on the top layer 24, and are then absorbed into the layer 21 in five to 30 seconds. The liquids diffuse through the bridge 20 and come into contact with each other at approximately equal distances from the holes 28 and 29, i.e., approximately at the center of the bridge 20. In this way, ion transport becomes possible, and a potential develops between the electrodes 10. Further, sufficient liquids to fill up the holes 28 and 29 are not absorbed into the layer 21 but remain in the holes 28 and 29.
Other examples of the materials preferable as the intermediate porous layer are described in Japanese Unexamined Patent Publication No. 52(1977)-142584.
Other examples of the bridge are described, for example, in Japanese Unexamined Patent Publication Nos. 55(1980)-59326 (U.S. Pat. Nos. 4,233,029 and 4,254,083) and 55(1980)-71942 (U.S. Pat. Nos. 4,217,119 and 4,302,313).
The ionic activity measuring device described above may be provided with many dry type, film-like electrodes having ion selective layers different from one another so as to measure activities of many different ions at the same time with one step of spotting the sample and the standard solution. However, studies conducted on this type of ionic activity measuring device revealed that it presents a very real problem as described below.
Namely, when the sample and the standard solution are applied to the holes of the bridge of the ionic activity measuring device provided with many electrodes, it is difficult for the liquids to be sufficiently distributed through the bridge and the respective electrodes by capillary action in a single liquid spotting step. Thus, it is difficult to measure the ionic activity in a stable manner. This problem is aggravated when the liquid has a high viscosity, as in the case of blood, and when the liquid transporting section involves a gap or an uneven level portion.